Is it her simple body plan? Her poker face? Or perhaps a vast mythology of her malevolence and supernatural abilities? Humans have a tough time describing what snakes do, let alone understanding why they do it. Proud skeptics that they are, scientists long doubted that snakes are capable of complex behavior. Reports of pitviper aggregations, especially mothers with young, are not new; but, until only recently, they were dismissed as happenstance, even by their biggest fanatics.
Arriving under cover of night in an amniotic sac, a newborn rattlesnake wriggles free of his membrane and opens his jaws to fill with a new atmosphere. Unfurling his tiny body, he mingles with his littermates, all new to this realm. As in humans, live birth in snakes is an abrupt transition from an aqueous medium to a gaseous one. But baby snakes are suddenly adept at locomotion, and with no worldly experience, one false move might catch the eye of all sorts of predators.
In this big, unforgiving world, is there anyone a newborn rattlesnake can trust? Why Mom, of course! While she no longer provides nourishment to her now-physically separate young, she will watch over and defend them when necessary, and may even corral them back to the nest if they wander too far. This attentiveness lasts a couple of weeks at most (when her babies cast off their first shed skins), but Mom has been in mom-mode for months already, often foregoing food while roasting her loins in the sun to ensure the proper and efficient development of her embryos.
Among the subtle mom-moves that we have observed (with the aid of cameras left to monitor nests) is her initial look out from the birth shelter (e.g., a rock, burrow or hollow log). On the first morning, Mom’s face peers out towards an adjacent sunny spot, where the babies will soon bask and explore during their first days. She’s probably looking for hazards, or maybe pointing the way, but after a couple minutes, her babies trickle out alongside her head. Though it is subtle, it appears to be communication (the transmission of information to influence another’s behavior). On subsequent mornings, Mom may repeat this behavior, but anxious babies become more apt to slip out before her.
Her young are eager for warmth, as heat cranks up their metabolism and hastens the shedding process. Mom, on the other hand, is not so keen to cook, as she has spent the better part of the active season staying hot to get the kids out on time. She may be content to stay in shade or even in the shelter, attentive to any commotion that might mean trouble. Defensive behaviors work well at a broad range of body temperatures, in contrast to the more heat-hungry biochemical processes like digestion, embryonic development and shedding, so even cool Mom is an effective guardian.
When Melissa and I monitor nests, we must balance not disturbing the snakes (overtly, at least) with getting images of behavior. If we get too close and cause someone to flee, we may set off a chain reaction among the snakes and disrupt their family time. However, such accidents reveal their real responses to perceived threats. Although a variety of factors probably influences a snake’s decision to escape (e.g., distance to shelter, body temperature, past experience), we have noticed a marked shift in a new mother’s tendency to react to our presence. During gestation, she tolerates us with near indifference, but once her babies are born, she often takes cover at the slightest provocation. Often (and only when babies are present) her head re-emerges. Is she making sure her young are still safe? And if not, would she confront the attacker?
The only nest attacks that we have witnessed were caught on camera while we were away. In both cases, each mother Arizona Black Rattlesnake emerged from cover to assume the rattlesnake threat posture (so often depicted in popular media). In one case, the attacker was a Rock Squirrel, a fairly large species we commonly see harassing resting snakes around basking sites (the second attacker was not captured on camera, but all three babies survived). Rock Squirrels often harass adult rattlesnakes, which appears to be more of an annoyance than a danger. We do not yet know how Mom would react to a more dangerous foe. Would she sacrifice herself to save her little ones?
In a very few cases, a mother has slowly emerged towards us as her babies disappeared into cover – the only times we’ve been “chased” by snakes. Although there is no coiling or rattling, the determined advance of a mother rattlesnake sends an unmistakable message: back off!
The presence of other adults appears to relieve Mom of some of her protective duties, as she seems more inclined to remain in shelter while her babies bask. The mere presence of these other adults may serve as a sufficient deterrent for many would-be baby snatchers, but do they take an active role in care (i.e., alloparent)? I’ve only seen it once: beside a still-pregnant Arizona Black Rattlesnake (Priscilla), a newborn (House, whose mother remained in shelter) squirmed and fidgeted beside her as I watched through binoculars. Soon, he began to crawl out into the open and in my direction. From her relaxed coil (she was accustomed to our visits), Priscilla darted out her head to intercept House’s advance, her face directly in front of his. He immediately stopped, paused briefly, returned to the shelter of the rock and coiled into stillness. Basking would have to wait.
After a week or two, newborn rattlesnakes cast off their neonatal skin. Their colors become more vibrant, their patterns sharper. With shedding comes increased sensitivity in vision and, presumably, touch. While they might linger a short time at the nest, nimbly crisscrossing their comparatively drab “pre-shed” siblings, a hunger propels them into the unknown. We begin to find them in tiny, coiled postures, propped against rocks and logs in anticipation of a passing lizard. Mom, too, is hungry, having given over the better part of her year to reproduction. In colder climates, only a few short weeks remain before the weather drives them underground for the winter. Fortunately for these new babies, they are able to follow Mom’s scent back to the same rocky sanctuary that may have protected this clan of snakes for a thousand winters.
More Rattlesnake Family Stories!
Mother’s day is a much bigger deal than Father’s day. Why? Well, there’s just something extra special about mom (sorry Dad!). So, today’s post is about an under-appreciated group of moms (you guessed it), Arizona Black Rattlesnakes!
“To endow animals with human emotions has long been a scientific taboo. But if we do not, we risk missing something fundamental, about both animals and us.” de Waal (1997)
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